1. Field of the Invention
This invention relates generally to a method and apparatus for exciting a light source, and more particularly to a method and apparatus for exciting a high intensity electrodeless light bulb.
2. Description of Related Art
In the field of electrodeless lamp technology, improvements are constantly being made on apparatus for generating high intensity light in a plasma generated and sustained by RF excitation. The lamp itself is generally well known and typically comprises a closed, transparent quartz light bulb filled with an inert gas and certain chemical elements. Typically, the gas is comprised of argon and element(s) selected from Group VI-A of the periodic table of elements, e.g. sulfur. Where sulfur is used as the material in the bulb and is heated by concentration of RF energy coupled thereto from an RF driver circuit, the inert gas is ionized and the elements contained therein are vaporized to form a high temperature plasma which emits high intensity light which is similar to bright sun light. As is well known, RF coupling to the bulb is provided through a coupling coil or other means, external to the bulb, in order to create and sustain the plasma.
For low power bulbs, in the order of 100-200 watts, the exciting RF frequency is typically between 10 MHz and 100 MHz, with a selection of frequency being determined by the effectiveness of coupling and Federal Communications Commission (FCC) frequency allocation.
The effective RF to light power efficiency of such a low power electrodeless lamp is determined, in part, by initial power input level to the bulb which is necessary to generate and heat the plasma before any light is emitted. This offset results in a net bulb efficiency characteristic which improves as power input to the bulb is increased. Thus, a penalty in efficiency is paid for low power bulb operation.